1. Field of the Invention
The present invention relates to an apparatus for the fabrication of models of teeth and their arrangement, especially so-called serrated models, with the teeth being detachably connected, either individually or in groups, with a base plate.
2. Description of the Prior Art
For various dental work, it is necessary to have a true-to-size tooth and jaw model, a so-called master model. To produce such a model, a plaster of Paris imprint is taken of the jaw of the patient. The tooth arrangement model that is obtained is generally secured to a base plate, which is generally also made of plaster of Paris. For certain dental work, for example when fitting crowns, caps, or bridges, it is desirable to be able to remove individual teeth, or groups of teeth in the form of segments, from the base plate, and to be able to accurately reinsert them after the work is complete. For this purpose, with conventional models, pins, so-called dowel pins, are provided, one end of which is fixedly connected to the tooth arrangement segments, with the other free end fitting into corresponding holes provided in the base plate. When the dowels pins are withdrawn from the holes, relatively high frictional forces result, preventing the segments from accidentally coming loose from the base plate.
Unfortunately, this dowel pin technology has, among others, the following drawbacks:
1. The pins must be disposed exactly parallel to one another, since this is the only way to provide for a problem-free removal and reinsertion of tooth arrangement segments. Relatively complicated and expensive pin-setting apparatus is used for placing the pins.
2. A precise seating of the individual tooth arrangement segments can be achieved only with difficulty, especially when the pins and holes become worn due to frequent removal.
3. Generally, the base plate can be used only once, since the pins and holes are precisely disposed relative to one another, and in practice it is not possible to insert pins into a tooth arrangement in such a manner that they will fit exactly in an existing base plate that is already provided with holes.
4. Models for crowns and bridges are generally made of wax. With all models where the tooth arrangement is held on the base plate by frictional forces, there exists the serious drawback that in order to remove the segments, relatively high frictional forces must be overcome. In so doing, tilting is unavoidable, so that damage to the parts that are modeled in wax can easily occur.
Attempts have already been made with such tooth models to dispense with the use of dowel pins. Without exception, all of the proposals for realizing this possibility also assured connection between the tooth arrangement and the base plate by using frictional forces. For example, European Patent application No. 44 223 discloses such a model, the tooth arrangement of which, on the underside, is provided with a pattern of parallel zig-zagged ribs in grooves. The upper surface of the base plate is provided with a pattern that is complementary to the pattern of the tooth arrangement. When the tooth arrangement and base plate are placed together, the ribs in grooves mesh with one another, thus assuring connection of the two parts via frictional forces. However, this proposal also results in the aforementioned difficulties. In particular, there exists the danger outlined above in paragraph number 4, namely damage to the model parts made of wax when the individual tooth segments are removed from the base plate.
An object of the present invention is to provide an apparatus for the fabrication of tooth arrangement models having removable tooth arrangement segments, with such segments being adapted to be secured to the base plate in a simple and precise manner without the seating of the segments becoming loose after repeated removal, and without there existing the danger of damaging models made of wax.